At the ECOO conference i met a man by the name of Rudy Neufeld. He has created a math resource software series called Understanding Math. It is very well designed, very user friendly, and most importantly, he envisions the software being used to COMPLEMENT the teacher's instruction and students' use of manipulatives. It truly is an enhanced learning experience, as opposed to a "stick a kid on a computer with this math game and leave me alone" kind of resource.
For more information, visit his website. You can view sample lessons, templates and other resources, as well as download samples of the software for classroom use.